A personal communication service (PCS) system is an example of a wireless communication system. A PCS system is intended to provide wireless service for low mobility applications, where users move relatively slowly over limited geographic areas. For example, a PCS system is intended to provide wireless service within business complexes, large buildings, commercial parks, city business districts, universities and the like, where a user may walk or otherwise move slowly in a limited area. Because a PCS system is specifically designed for low mobility applications, the system does not require the extensive and expensive infrastructure of a wireless telecommunication system.
A PCS system may be a part of a telecommunication network as illustrated in FIG. 1.
A PCS system or network of the prior art includes a network database 100, PCS switching systems 200, and a switched telephone network 300, for example, a public switched telephone network (PSTN) or an Integrated Signaling Digital Network (ISDN).
The network database 100 includes a Home Location Register (HLR) 50, which contains wireless subscribers' profile information. Subscribers' profile information includes information such as address, account status, preferences, etc. Each PCS switching system 200 includes a PCS switching center or station 30, and a plurality of radio port control units (RPCU), also known as cell stations 20. Each cell station 20 is connected to a switching station 30 via, for example, a basic rate interface (BRI) line 25. A signal protocol between the switching station 30 and the cell station 20 may be the Q.931 signaling protocol. Each of the cell stations 20 controls a radio port having a radio transmitter/receiver to communicate with mobile stations 10 located in a geographic service area served by that cell station 20. Several cell stations 20 may be arranged such that their service areas are contiguous and provide an extended range of service beyond the geographic area served by a single cell station 20.
The network database 100 is connected to the switching stations 30 via a switching transfer point (STP) 60. The STP 60 is responsible for signal transfer between a switching station 30 and local offices 70, or among different switching stations 30. The local office 70 may further be connected to analog lines 80 and customer premise equipment (CPE) 90 as shown in FIG. 1.
A switching station 30 may be a conjoining point of the PSTN/ISDN network 300 and the PCS switching system 200. Accordingly, a switching station 30 may also serve as a wireless switch and serve a plurality of subscribers, including the analog lines 80 and CPE 90, similar to a local office 70 as shown in FIG. 1.
The cell stations 20 serving contiguous geographic areas may be connected either to the same switching station 30 or to different switching stations 30. When a mobile station 10 moves between areas served by cell stations 20 on the same switching station 30, the transfer of service from a current cell station 20 to a new cell station 20 is known as an intraswitch handover or an intraswitch automatic link transfer (ALT). When the mobile station 10 moves between geographic areas served by cell stations 20 hosted by different switching stations 30, the transfer of service from the current cell station 20 to the new cell station 20 is known as an interswitch handover or an interswitch ALT.
If a user makes/receives a call via a first switching station 30 and then is handed over (interswitch) to a second switching station 30, the second switching station 30 begins handling dual tone multi-frequency (DTMF) requests. Also the first switching station 30 stores the call-related information (e.g., call forward, call hold, etc.), which is unknown to the first switching station 30. Accordingly, this type of interswitch procedure may introduce errors when handling DTMF requests as will be discussed in more detail below with respect to FIGS. 2a-2c. 
FIGS. 2a-2c illustrates an interswitch handover in a PCS system of the prior art.
Referring to FIG. 2a, a mobile station 10 continuously monitors signals when the mobile station 10 is in a first cell station 20a of a first switching station 30a. If the signal from the first cell station 20a falls below a certain threshold, the mobile station 10 transmits a handover request message through an air interface protocol 34 to a second cell station 20b of a second switching station 30b (assuming that the second switching station 30b is transmitting a stronger signal than the first switching station 30a) as shown in FIG. 2b. 
The second cell station 20b sends a handover request message to the second switching station 30b via the BRI line 25. When the second switching station 30b receives the handover request message, the second switching station 30b stores information about the second cell station 20b, and then queries 45 a home location register (HLR) 50 for information on the first switching station 30a via the STP 60. Using this information, call setup message 36 is sent from the second switching station 30b to the first switching station 30a to request a voice path switch as shown in FIG. 2c. The first switching station 30a sends an acknowledge message 37 to the second switching station 30b, and performs a voice path switch operation to the second switching station 30b. In the prior art, the first switching station 30a is only responsible for the voice path switch operation during the interswitch handover.
The prior art provides no measures for the following scenarios. Referring again to FIG. 2c, during an interswitch handover, but before the second switching station 30b receives an acknowledge message 37 from the first switching station 30a, a mobile station 10 may send DTMF requests via the air interface protocol 34 through the second cell station 20b to the second switching station 30b. However, the second cell station 20b will ignore the DTMF requests because a voice path has not been fully connected, which may cause certain DTMF digits to be missing during the interswitch handover. For example, a user calls a Private Branch Exchange (PBX) number, and hears an announcement prompting to enter an extension number, such as “12345”. However, if a call of the mobile station 10 is handed over while the user starts to enter the extension number, the user may enter “12” while in the first switching station 30a and enter “345” while in the second switching station 30b. Because the second switching station 30b ignores DTMF requests during an interswitch handover, the digits received by the PBX switch is “12” and the user (mobile station) will either be connected to an extension “12” or get a vacant number announcement.
Referring to FIG. 2d, after an interswitch handover, a mobile station 10 may send DTMF requests via the air interface protocol 34 through the second cell station 20b to the second switching station 30b for supplementary services, for example, a conference call, a call transfer, a call hold, etc. For example, the dialed digits “*69” may represent the trigger for a call back service. The second switching station 30b may receive the “*69” trigger, but because the second switching station 30b has no call-related information with respect to the supplementary services of the mobile station 10, the second switching station 30b will treat the DTMF requests as playing tones only towards the network. The mobile station 10, therefore, may lose such services after an interswitch handover.